The Sound of Electrons Shattering: Current Noise Composition Laws for Electron Fractionalization

Abstract

We develop a theory of the non-equilibrium current response for metallic systems near quantum critical points where electronic quasiparticles fractionalize, such as systems near continuous metal-insulator transitions or composite Fermi liquid to Fermi liquid transitions. Applying a generalized response theory within a Keldysh path integral framework, we derive a non-perturbative current noise composition law, wherein the total noise is the sum of the noise of each fractionalized constituent (bosonic holons and fermionic spinons), weighted by their respective resistivities. We demonstrate that the formally derived composition relations can be interpreted in terms of a simple analogy with resistors in series. We leverage this composition rule near certain quantum critical points to show that the shot noise can be suppressed in long nanowires as compared to Fermi liquid expectations due to the collusion of quantum criticality with fractionalization.

Figures (1)

• Figure 1: (a) Electronic quasiparticles coupled to an external EM field $A$ fractionalize into neutral fermionic spinons, $f$, and bosonic charge-carrying holons, $b$, interacting through an emergent $\mathrm{U}(1)$ gauge field, $a$. The key results of this work can be understood via a circuit analogy with resistors in series, with respective resistivities $\rho_f$ and $\rho_b$ corresponding to spinons and holons. (b) Schematic plot of measured current $I$ as a function of time $t$, showing the first moment (average current) and second moment (current noise).